The combustion of fossil fuels in activities such as the electricity generation, transportation, and manufacturing produces billions of tons of carbon dioxide annually. Research since the 1970s indicates increasing concentrations of carbon dioxide in the atmosphere may be responsible for altering the Earth's climate, changing the pH of the ocean and other potentially damaging effects. Countries around the world, including the United States, are seeking ways to mitigate emissions of carbon dioxide.
In order to capture carbon dioxide from industrial sources, such as a coal-fired power plant, the carbon dioxide is separated from flue gases, which are primarily nitrogen and water and include other trace gases, metals and particulates. Previous work in the field has many limitations, in particular the energy consumed in separating the carbon dioxide from the other gases and the amount of water used in the separation. A common technique currently available uses monoethyl amine (MEA) adsorption of the carbon dioxide from the flue gases. However, the technique utilizes high temperature steam to effectively separate the carbon dioxide from the amine. As such, the technique can consume as much as 30% of the energy generated at a coal-fired power plant. Furthermore, carbon dioxide capture increases both the amount of water that is brought into a power plant and the amount of water evaporated into the atmosphere by the power plant. Adding the carbon dioxide capture can increase the water brought into the power plant by 2300 to 4500 liters per megawatt-hour. Increased water evaporation from the power plant due to the carbon dioxide capture can range from 1900 to 3400 liters per megawatt-hour.
Work has also been done on electrochemical systems, such as electrodialysis via carbonates, to separate the carbon dioxide from the other gases. The electrochemical systems have slow kinetics and low efficiency making the systems uneconomical. Membrane separation of the carbon dioxide is possible, but no effective membranes have been made to date. Carbon dioxide is also removed by cooling the flue gas until dry ice is formed. However, the energy used in the process is higher than for amine adsorption.
Existing processes incorporating ethyl amines or other absorbents use large quantities of energy and water that make such techniques uneconomical. Membrane systems lack the strength and/or stability to last for long periods of time. Membrane systems and electrodialysis systems also have slow rates of reaction making upscaling difficult economically.